Chaser assembly



June 23, 1942. F, NELL CHASER ASSEMBLY Filed May 22, 1940 Frederic Nel/ Patented June 23, 1942 UNITED STATES 'ATENT OFFICE GHASER ASSEMBLY Application May 22, 1940, Serial No. 336,666

19 Claims.

This invention relates to circular chaser assemblies such as are employed on taps and die heads.

cutting position for any particular diameter, or

for resetting them to the same diameter after they have been ground for re-sharpening purposes.

In my prior patent, No. 2,120,621, granted June 14, 1938, I disclosed an invention which marked a decided forward step'in the design and usefulness of circular chaser assemblies, as it embodied means for rigidly securing the chasers to the holders and yet afforded means for adjusting the chasers by small amounts-Without removing them from the holders, through the use of an adjustable finger. In some classes of service, however, my prior assembly is open to certain disadvantages. The chief defect of my prior assembly is the tendency to break the finger member thereof through causes other than the excessive stresses under which it was expressly designed to be broken. I have found that it is impossible to obtain or heat treat a metal so that the finger is sufiiciently tough as to withstand considerable but unexcessive surge stresses, and yet has a sufficiently hard'sur'f-ace to resist the abrasion occasioned by the cooperating screws. Repeated adjustments sometimes result in wearing away or "necking down the central portion of the finger, so that it snaps under loads which it was originally designed to resist.

My present circular chaser assembly does not employ a safety device which is quite so sensitive; however, it does provide a reasonable degree of safety against breakage of the chasers or holder parts, and in addition is so designed that wear will not unduly Weaken my adjustment member. Further, my entire assembly now is more adapted to economical machining because fewer parts are employed, and they do not involve any special or exacting consideration, due to their particular shape.

The very simplicity of my present structure has inherent advantages from the operating standpoint because the device is self-locking, requiring the operator to expend but a very minimum of time to secure the desired adjustment. Further,

the chaser may be reground without removing it from the holder, and a major adjustment then made to reposition it in the proper cutting posi tion in but a fraction of the time formerly employed.

Accordingly, it is the primary object of my invention to provide a'novel chaser assem ly which is very simple in construction, very precise in ad justment, very rugged under all operating conditions, and yet which incorporates reasonable safety measures to avoid the breakage of more costly parts thereof.

It is afurther important object of my invention to provide a circular chaser assembly having adjustment means which require a minimum expenditure of the operators time and effort to eifect both minor cutting adjustments and major adjustments, such as are necessary after repeated regrindings of the chaser.

Another object is to provide a circular chaser assembly having means for effecting coarse or major adjustment of the chaser in equal increments, and a fine adjustment for securing a final or rake angle adjustment of the chaser.

It is a further object to provide a chaser assembly having a single, rotatable self-locking member for effecting minor adjustment of each chaser.

Another object of my invention is to provide a novel circular chaser assembly which is equally adapted for use in taps or die heads.

A further object is to generally improve and refine certain details of the chaser assembly shown in my prior patent.

Further objects of my invention will be apparent from the following description thereof when taken in conjunction with the accompanying drawing and from the appended claims.

In the drawing,

Figure 1 is a longitudinal sectional View of one of my novel circular chaser assemblies;

Figure 2 is a view looking from the left hand side of Figure 1, with the chaser removed and with certain parts broken away and in section to more clearly illustrate the construction;

Figure 3 is an enlarged cross-sectional view showing part of my adjustment mechanism disposed in one extreme adjusted position;-

Figure 4 is a view similar to Figure 3, but shows my adjustment mechanism disposed in the opposite extreme adjusted position;v

Figure 5 is a front View of the assembly; and

Figure 6 is a fragmental, enlarged sectional view showing the cooperating serrations of the bushing members.-

Referring to Figures 1, 2 and 5, circular chaser i0 is mounted upon a holder II. The latter is provided with a camming element l3 for coaction with the camming member of a die head or tap to move the said holder l I radially inward or outward, and also has-a guide 9 adapting it for sliding movement on a die head or tap. These features are shown morefully in my prior patent,

No. 2,100,449, granted November 30, 1937, and as they form no part of the present inventicn, they will not be further described.

A clamping screw 54 is utilized to fasten chaser Hi to holder I I, the latter having a threaded bore for receiving said screw. It should be noted that screw l4 maintains the under surface 22 of chaser S in firm engagement with the upper surface 2! of holder H, thereby assuring that the threadcutting serrations of chaser iii are properly located with respect to surface 2 l.

Holder H is accurately counterbored to receive a lower or adjusting bushing member 3 l and the flange of an upper bushing member '35, which rests thereupon. Bushings Stand-3,1 are-adapted to be locked against relative rotation by serra tions 82 on member 3! and serrations on member 31. Upper bushing 3! is providedalso with a pilot surface which coacts with a cylindrical surface in chaser it to very accurately center the chaser and to prevent any radial play'thereof. Thus, chaser surfaces 26 and 4!! and the flange of bushing 3!, very ac:;urately determine the relationship between the thread-cutting ser rations 25 and the work.

Chaser I9 has a splined bore which coacts with splines 5| on bushing 3| to lock the chaser to the bushing. Thus, any angular adjustment of lower bushing or adjustment bushing 30, through interfitting serrations 32 and33 results in an exactly equal angular adjustment of bushing 3|, and since the latter is coupled -'to the chaser by splines 5|, this results in effecting a similar angular adjustment of the chaser.

To effect such adjustment, holder H has a bore 60 in which is located an adjustment pin 65 having at one end a reduced, slightly eccentric extension 55, which fits into a recess 51 in adjustment bushing 30. The other end of adjustment pin 65 rests against a counterbored face 69 in bore 68 and is provided with a suitable socket TG for an adjusting wrench. The wrench may be applied to socket [0 from the rear of the holder after the latter has been'removcd from the die head or tap.

When it is desired torotate chaser [0 to effect a minor angular adjustment thereof, such as is necessary to establish the correct relation between the thread-cutting serrations 25 and the work, adjustment pin 65 is rotated the proper amount to cause eccentric end to efiect the proper degree of rotation of adjustment bushings SB and 3!, and chaser ID. 'The amount of adjustment which can be secured by rotating pin 65 from one extreme position to another (through 180 degrees) is but slightly greater than the pitch of the serrations 32 and 33 (see Figures 3 and 4) consequently, very accurate adjustments can be effected. Further, the slight amount of eccentricity of end 66 of pin -65 is sufiicient to render the arrangement self-locking. In other words, no matter how great the forces developed in the chaser during the thread-cutting operation, bushing 30 cannot effect rotation of the eccentric 6'6, no matter what angular position it may assume. Even when the center of ec'cen trio portion 65 is disposed directly above or'below the axis of the body 65, the assembly nevertheless is self-locking, This is readily understood when it is realized that the degree of oilset of the two axes is so'small, that-any turning moments applied to portion fifi result in the development of high frictional forces at the point of engagement of the adjustment bushing with portion 65, and also between bore and body 65, which accordingly produces a resistance moment of greater magnitude than the turning moments applied. In other words, the greater the turning moment applied, the greater will be the resulting frictional resistance moment. Consequently, it is apparent that adjustments can be made with a minimum of time and effort, for a slight rotation of pin is all-that is required, and that the adjusting pin is self-locking.

When it is required to resharpen the threadcutting serrations 25, the operator need only loosen clamping screw [4 a sufiicient amount to permit the adjustment serrations 3| and 33 to disengage. The fit-between the chaser bore 49 and pilot surface :35 is so close that when the "chaser is lifted the adjustment bushing 31 is carried therewith. The chaser and adjustment bushing then are rotated the pitch of one or more adjustment serrations and the adjustment serrations 32 and 33 again are permitted to engage. 'It is apparent that the smallest adjustment possible is the pitch between any two adjacent serrations.

Thus, the chaser H] can be sharpened without removing it from holder H, and a minimum of loosening of the parts is involved. In former assemblies it was necessary to loosen the screw l4 sufficiently topermit the splines 59 and5l to be disengaged; consequently, there was little saving of timea'n'd effort as'compared to removing thechaser entirely fromthe holder. The relatively shallow depth of serrations 32 and '33 eliminates this disadvantage, while the multiplicity employed assures economical tool life because the chaser can be adjusted by very small angular increments. Moreove'n'since pin 65 may be used to angularl adjust the chasers from an infinitely small angle to an angle greater than that corresponding to the pitch of one adjustment serration, it is not necessary to grind the chasers, with respect to the serrations or any fractional part thereof; however, when a considerable amount of the chaser needs to be ground away to sharpen it,my present arrangement makes it possible to do so with a minimum of time and effort. 'Pin65also provides an extremely precise rake angle adjustment of the chasers.

Although'I have shown bushing member 3| as being-separate from, and splined'to, chaser l0,

a as a dvanta'geous'in assemblies in'which bushing 3! and chaser Ill are combined as a single integral element, and the appended claims are intended to embrace the invention where it is so employed.

The safety feature ofthe'pre'se'nt invention resides in giving eccentric 66 an effective crosssectional area which is somewhatlessthan either (l) the effective shearing area of serrations 32 and 33, or ('2) the effective shearing area of splines 5!. Therefore, should the machine be subjected to destructive -fo'rc es, eccentric 66 will shear off, thereby protecting the more costly parts of the machine. Ih'a've found'that by using a shearable pin, "the apparatus will maintain an providing shoulder 69 in bore 60, and a' blind recess fi'l in bushing 30, pin 65 is securely restrained agai'nst accidental endwise displacement from the holder, and yet it may be readily removed when desired by removing the chaser and bushings from the holder.

Referring to Figures 1 and 6, serrations 32 and 33 are preferably provided with slant and straight sides and are so disposed that when cutting forces developed in the chasers result in a tendency to move bushing 3| in the direction indicated in Figure 6 by the arrow, the turning moment is taken by the straight or axially directed portions of the serrations. This precludes the development of axially directed forces which might tend to lift face 20 of the chaser off of the holder.

It is also to be understood that the novel chaser assembly of the invention is equally useful in dies as well as taps, the only change necessary being to rotate the chasers through approximately 180, to dispose their cutting edges inwardly rather than outwardly, and moving them outwardly the required distance to cut a thread on the external rather than the internal surface of the work, to thereby adapt them for threading an external, rather than an internal surface, and the appended claims are intended to cover the chaser assembly irrespective of whether it is used in a tap or die.

From the foregoing it is apparent that the present invention constitutes an efficient threadcutting mechanism of extremely simple construction, having relatively few parts; it is very precise in adjustment, the adjustment being infinitely variable by small increments; it is very rugged, all the moving parts having considerable bearing areas; it provides a reasonable safety feature in the form of a shearable adjusting pin, which is not subjected to localized wear; and it is so designed that a bare minimum of time and eii'ort is required to effect either minor or major chaser adjustments.

The invention may be embodied in other specific forms Without departing from the spirit or essential characteristics thereof. The present embodiment is, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing it description. and all changes which come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.

What is claimed and desired to be secured by- United States Letters Patent is? 1. In a thread-cutting device, a chaser holder; a circular chaser assembly mounted on said holder for limited rocking movement about a fixed axis; and means for rocking said chaser about .3

said axis, comprising a self-locking rotatable device, having an eccentric portion, mounted in said holder and operably connected to said chaser assembly.

2. In a thread-cutting device, a holder; a circular chaser assembly mounted on said holder for limited rocking movement about a fixed axis; and means for rocking said chaser assembly about said axis, comprising a pin mounted for rotation about an axis spaced from and parallel to said fixed axis and having an eccentric head seating in a recess in said chaser assembly.

3. In a thread-cutting device, a holder havin a pair of parallel openings therein; a chaser assembly; a screw threaded into one of said openings and mounting said chaser assembly for rocking movement on' said holder; an adjusting pin mounted'for rotation in said other opening and having an eccentric end engaging a recess in said chaser assembly; and a shoulder on said holder cooperating with the other end of said pin for limiting axial movement of said pin away from said chaser assembly.

4. A circular chaser assembly comprising a chaserholder; a circular chaser mounted on said holder; a chaser bushing; means for non-rotatably coupling said chaser bushing to said chaser; an adjustment bushing adjustably secured to said chaser bushing; and means for efiecting rotation of said adjustment bushing with respect to said holder.

5. A circular chaser assembly comprising a chaser holder; a circular chaser mounted on said holder; a bushing coupled'to said chaser; an adjustment bushing coupled to said first bushing; and means for effecting rotation of said adjustment bushing, comprising a rotatable pin mounted in said holder and having an eccentric and coacting with a recess in said adjustment bushing.

'6. A circular chaser assembly comprising: a chaser holder; a circular chaser mounted on said holder; a bushing located between said chaser and said holder and having splines coacting with similar splines located in'said chaser; an adjustment bushing having adjustment serrations coacting with adjustment serrations located on said first-named bushing; and means for eifecting rotation of said adjustment bushing into any one of a plurality of angular adjusted positions.

7. A circular chaser assembly comprising: a chaser holder; a circular chaser mounted on said holder; a bushing having splines coacting with similar splines located in said chaser and having a pilot coacting with a bore-in said chaser; an adjustment bushing having adjustment serrations coacting with adjustment serrations located on said first-named bushing; and means s for effecting rotation of said adjustment bushing, comprising a rotatable pin coacting with said adjustment bushing and capable of rotating the same an angular distance greater than the pitch of said adjustment serrations.

8. A circular chaser assembly comprising: a chaser holder; a circular chaser mounted on said holder; a bushing having splines coacting with similar splines located in said chaser and having a pilot coacting with a bore in said chaser; an adjustment bushing having adjustment serrations coacting with adjustment serrations located on said first-named bushing; and means for effecting rotation of said adjustment bushing; said means comprising a rotatable pin having a reduced, eccentric end coacting with a recess in said adjustment bushing, the eccentricity of said reduced end being greater than the pitch of the said adjustment serrations.

9. A circular chaser assembly comprising: a chaser holder; a circular chaser assembly mounted on said holder and having adjustment serrations coacting with adjustment serrations located on an adjustment bushing; and means for effecting rotation of said adjustment bushing, comprising a self-locking, rotatable pin located in said holder and having an eccentric end coacting with a recess in said adjustment bushing, the eccentricity of said reduced end being greater than the pitch of said adjustment serrations, but insufficient to effect undesirable oounter-rotation of said pin in response to cutting forces developed in said chaser.

10. In combination, a chaser holder; a circular chaser; means supporting said chaser for rotational adjustment on said chaser holder; means for efiecting major angular adjustment of said chaser; and means for eiiecting minor angular adjustment of said chaser; said latter means comprising an eccentric pin mounted for rotation in said chaser holder, and coacting with said means for effecting major angular adjustment of said chaser.

11. In combination, a chaser holder; a circular chaser; means supporting said chaser for rotational adjustment on said chaser holder; means for efiecting major angular adjustment of said chaser; and means for effecting minor angular adjustment or said chaser; said latter means comprising a pin having an eccentric end cooperatin'g With a recess in said means for supporting said chaser, and whose eccentricity is at least equal to the smallest adjustment which can be eifected by said means for efiecting major adjustment of said chaser.

12. A chaser holder, a chaser on said holder; means for effecting major rotational adjustment of said chaser by fixed increments; means for effecting minor rotational adjustment of said chaser; said latter means comprising a self-locking eccentric mechanism operably associated with said chaser holder and having sufficient eccentricity to efiect rotational chaser adjustment at least equal to the increments of adjustment effected by said major adjustment means, but having insufiicient'eccentricity to permit counterrotation of said eccentric mechanism through rotative stresses imposed on said chaser.

13. In combination, a chaser holder having a circular chaser mounted thereon; means for supporting said chaser in desired relation with respect to said holder, comprising a member secured to said holder and connected to said chaser by splined surfaces, said member further having adjustment serrations located thereon; and means for effecting rotational adjustment of said chaser, comprising a pin with a reduced, eccentric end, said reduced end having less shearing area than the shearing area of said splined surfaces and of said adjustment serrations.

1.4. A circular chaser assembly comprising: a chaser holder having a circular chaser mounted thereon; a chaser bushing disposed between said holder and said chaser and splined to said chaser; an adjustment bushing disposed between said holder and said chaser bushing and having adjustment serrations coacting with similar serrations located on said chaser bushing; and means for effecting rotational adjustment of said adjustine'nt bushing, the height of said adjustment serrations being considerably smaller than that of said splines, whereby said serrations may be disconnected to adjust said chaser without disconnecting said chaser from said chaser bushing.

15. In a chaser assembly, a holder; a chaser device mounted for limited rotation on said holder and having a plurality of serrations projecting toward said holder; a member disposed between said chaser device and said holder and having serrations interfitting With said first-named serrations; and an eccentric pin cooperating with a recess in said member for adjusting said chaser angularly with respect to said holder, said pin having less efiective shearing cross-sectional area than said serrations.

16. In a thread cutting device, a chaser holder, a circular chaser assembly mounted on said holder for limited rocking movement about a fixed axis, and having a pair of spaced walls, offset from said axis; and means for rocking said chaser about said axis, comprising a member having opposed curved surfaces having a common center of curvature and coacting with said walls, said member being mounted for rotation on said holder about an axis substantially parallel to said fixed axis and located between said opposed curved surfaces,'but being offset from the common center of curvature thereof.

17. The thread cutting device defined in -claim 16, wherein said walls are formed in a disc-like element, and said member is located substantially wholly within the periphery of said disc-like element.

18. In a thread cutting device, a support; a circular chaser assembly mounted on said support for rocking movement about a fixed axis; and means for rocking said chaser assembly about said axis, comprising a member rotatable about an axis spaced from and disposed substantially parallel to said fixed axis and having an eccentric portion seating in a recess provided in a part operably connected to said chaser assembly and operable to rock said chaser assembly when said member is rotated about its axis.

19. In a thread cutting device, a chaser holder; a circular chaser assembly mounted on said holder for limited rocking movement about a fixed axis; and means for rocking said chaser about said axis, comprising a self-locking rotatable device, having an eccentric portion, mounted in said holder and operably connected to said chaser assembly, the eccentric portion of said device being adapted to be sheared by excessive stresses acting upon said chaser before any detrimental distortion thereof occurs.

FREDERIC NELL. 

